1. Field of the Invention
This invention relates to the formation of a molded block of dilute high explosive foamed polyurethane. More particularly, this invention relates to an improved process, composition, and apparatus for the formation of a molded block of dilute high explosive foamed polyurethane.
2. Description of the Related Art
The formation of molded explosives incorporated into foamable plastic materials is known. For example, Stark U.S. Pat. No. 2,768,072 describes the formation of a foamed explosive using either a foamed thermosetting polyester resin cross-linked with styrene, a polyurethane foam resin formed from toluene diisocyanate and alkyd resins, a foamed polyvinyl chloride, or a foamed epoxy resin.
Stark U.S. Pat. No. 2,845,025 also discloses a foamed explosive using a thermosetting polyester resin using however, methyl methacrylate, either in monomeric or polymeric form, instead of styrene, as the cross-linking agent.
Thomas U.S. Pat. No. 3,198,677 describes a solid self-combustible cellular organic polymer composition in which the composition forms the cells walls of an integral foamed cellular structure. The self-combustible composition comprises an inert organic polymer binder, such as foamed polyurethane; and a finely divided oxidizer, such as pentaerythritol tetranitrate (PETN), dispersed in the binder.
Donaghue et al. U.S. Pat. No. 4, 15 1,022 discloses an explosive composition wherein a particulate explosive is dispersed in a foamed non-explosive matrix such as polyurethane.
Sanai U.S. Pat. No. 4,722,280 describes the formation of a molded low density explosive member by first mixing together an explosive powder and polystyrene beads, and then heating the mixture to foam the polystyrene beads to form the molded low density structure.
In some respects, processes which involve the use of thermosetting reactants such as, for example, the above described processes for forming a foamed polyester, epoxy, or polyurethane matrix for the explosive, are preferred over the use of foamable thermoplastics such as foamable styrene, because no heat need be supplied to the system. However, the amount of heat generated by such exothermic processes, and the need to somehow control the temperature of the thermosetting reaction while such heat is being generated, introduces additional safety problems when one is forming explosive materials.
For example, temperatures in excess of 230.degree. C. may be encountered during the exothermic reaction to form a foam polyurethane, while the melting point of pure pentaerythritol tetranitrate (PETN) is only 141.degree. C.
Therefore, while the prior art describes the formation of explosive compositions using foamed thermosetting organic binders such as polyurethane, in actual practice, safety considerations have inhibited the formation of molded foamed explosive blocks using organic binders such as polyurethane with explosives such as pentaerythritol tetranitrate, because of the excessive exothermic heat generated during formation of such a molded foam explosive.